patch 7.4.2090
Problem:    Using submatch() in a lambda passed to substitute() is verbose.
Solution:   Use a static list and pass it as an optional argument to the
            function.  Fix memory leak.
diff --git a/src/channel.c b/src/channel.c
index ae5bdf2..722dcb8 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -1533,8 +1533,8 @@
     argv[0].v_type = VAR_CHANNEL;
     argv[0].vval.v_channel = channel;
 
-    call_func(callback, (int)STRLEN(callback),
-			&rettv, 2, argv, 0L, 0L, &dummy, TRUE, partial, NULL);
+    call_func(callback, (int)STRLEN(callback), &rettv, 2, argv, NULL,
+					  0L, 0L, &dummy, TRUE, partial, NULL);
     clear_tv(&rettv);
     channel_need_redraw = TRUE;
 }
@@ -2695,7 +2695,7 @@
 	      argv[0].v_type = VAR_CHANNEL;
 	      argv[0].vval.v_channel = channel;
 	      call_func(channel->ch_close_cb, (int)STRLEN(channel->ch_close_cb),
-			   &rettv, 1, argv, 0L, 0L, &dummy, TRUE,
+			   &rettv, 1, argv, NULL, 0L, 0L, &dummy, TRUE,
 			   channel->ch_close_partial, NULL);
 	      clear_tv(&rettv);
 	      channel_need_redraw = TRUE;
@@ -4758,7 +4758,7 @@
 	    argv[1].v_type = VAR_NUMBER;
 	    argv[1].vval.v_number = job->jv_exitval;
 	    call_func(job->jv_exit_cb, (int)STRLEN(job->jv_exit_cb),
-			   &rettv, 2, argv, 0L, 0L, &dummy, TRUE,
+			   &rettv, 2, argv, NULL, 0L, 0L, &dummy, TRUE,
 			   job->jv_exit_partial, NULL);
 	    clear_tv(&rettv);
 	    --job->jv_refcount;